<!DOCTYPE html>
<html lang="en">
    <head>
        <meta charset="utf-8">
        <title>Hello World</title>
        <script src="http://code.jquery.com/jquery-1.12.4.js" 
        integrity="sha256-Qw82+bXyGq6MydymqBxNPYTaUXXq7c8v3CwiYwLLNXU="
        crossorigin="anonymous"></script>
        <script>
            //1.原生js固定写法
            window.onload=function(ev){}

            //jQuery的固定写法
            $(document).ready(function(){
                alert("hello world");
            });
        </script>
        </head>
     <body></body>
    
</html>